1. Field Of The Invention
The invention relates to a fluid power actuator comprising a cylinder barrel containing a piston and having end caps through one of which the piston rod extends and of which both have tie rod openings to accept tie rods connecting the end caps with each other to clamp them onto ends of the cylinder barrel.
2. Brief Description Of The Prior Art
Cylinder actuators of this type are in widespread use, largely used for applications where they are subjected to substantial forces. In many such applications, as for example in packaging machinery or for table presses whose tool has to be precisely guided, there is the additional requirement of preventing twisting of the piston rod about its axis. One suggestion for effecting this has been to have a piston rod with a square or oval cross section to to have two parallel piston rods. However, such customized designs are complex to manufacture and therefore relatively expensive. Furthermore, they do not comply with ISO standard dimensions so that it is not possible to guarantee compatibility in every case.
In the German Gebrauchsmuster Pat. No. 8,307,197 an actuator without tie rods has been proposed in which twisting of the piston about its axis was to be prevented by the use of a guide rod connected with the piston and with a bearing on the radial outer face of one of the end caps so that the rod only moved in a direction parallel to the axial direction of the piston rod. However, this means for preventing rotation of the piston would not be suitable for combination with an actuator of the initially mentioned type. Even in the case of combination with a conventional actuator without tie rods, the result is a relatively large overall breadth of the actuator arrangement and if the system for preventing piston rotation were to be employed with an actuator of the initially mentioned design the breadth would be substantially increased, since such an actuator is provided with end caps with an inherently larger diameter in order to make it possible for the tie rods to be connected therewith. A further point is that in the case of such a combination of the guide rod at a relatively large distance from the outer face of the cylinder the rod would be in an exposed position so that if there were a shortage of space there would be a danger of the guide rod bending, something that would prevent proper use of the actuator. A combination of the actuator of the initially mentioned construction with the known anti-twist means of the said German patent would therefore have the consequence that there would be an unfavorable change in the dimensions of the actuator and this would be unacceptable in the case of the said special fields of application since in such a case the important aim is to produce an actuator which combines extremely high mechanical load carrying capacity with the greatest possible degree of compactness.